Project Summary/Abstract Development of precise control over stem cell function in vivo remains a major medical challenge, but there is not yet a complete understanding of how stem cell microenvironments naturally activate appropriate tissue repair mechanisms. Planarian flatworms possess an exquisite level of control over adult stem cell function that enables regeneration of any missing tissues following injury, even after decapitation. This ability relies on a pool of pluripotent adult stem cells, termed neoblasts, which can undergo self-renewal and also respond to signals from their microenvironment to control cell differentiation. For example, planarians have the capacity to specify the identity of missing tissue at wounds along the anteroposterior axis, a phenomenon known as regeneration polarity, in order to regenerate a head or tail at appropriate injury sites. Interestingly, I have identified one gene, protein tyrosine kinase-7 (Smed-ptk7) that is required for appropriate patterning along the anteroposterior axis during planarian organ regeneration. This research proposal aims to 1) identify a stem cell-dependent process regulated by protein tyrosine kinase-7 in organ regeneration and 2) identify the positional information system involving protein tyrosine kinase-7, Wnt, and Hox genes that enables proper organ regeneration. Functional assays including Smed-ptk7 RNAi treatment to examine neoblast behavior will define the cellular activities for Smed-ptk7 on the planarian stem cell population during organ regeneration. Additionally, double-RNAi experiments will assess the candidate pathway of action involving Smed-ptk7 and wnt signaling or hox activity to regulate positional identity during organ regeneration. Studies aimed at understanding how specific long-range molecules cell nonautonomously regulate stem cell behavior to re-establish proper form and function during organ regeneration could reveal ways in which injured tissue in other organisms instruct stem cells during regeneration.